Disc and facet replacement

ABSTRACT

An artificial disc for replacement of a spinal three-joint complex of a mammal includes a generally spinal disc-shaped upper plate having an anterior section and a posterior section and a generally spinal disc-shaped lower plate also having an anterior section and a posterior section. The anterior section of the upper plate is selectively separable from the posterior section of the upper plate and the anterior section of the lower plate is likewise selectively separable from the posterior section of the lower plate. A ball is interposed the lower face of the upper plate and the upper face of the lower plate and a plurality of posts, each projecting from one of the faces toward the other of the faces corresponds to a plurality of detents provided on the one of the faces opposite the face from which the corresponding post projects for engaging the posts.

RELATED APPLICATION

This present application claims all available benefit under 35 U.S.C. §119(e) of co-pending U.S. provisional patent application Ser. No.60/720,414 filed Sep. 26, 2005. By this reference, the entire disclosureof U.S. provisional patent application Ser. No. 60/720,414, includingthe drawings, is incorporated herein as though now set forth in itsentirety.

FIELD OF THE INVENTION

The present invention relates to medical devices. More particularly, theinvention relates to an artificial intervertebral disc and facetreplacement that very closely approximates the function of a naturalthree-joint disc and facet complex and that may be placed or extractedfrom or to either the anterior or posterior of a patient under treatmentas may be medically determined to be appropriate and, in the case ofextraction, without regard for whether the disc and facet replacementwas placed from the anterior or posterior.

BACKGROUND OF THE INVENTION

Deterioration through disease or damage from injury often necessitatesthat a patient undergo surgical intervention for the removal of his orher natural three-joint disc and facet complex and replacement thereofwith an artificial disc. Unfortunately, the available artificial discsdo not generally well approximate the function of a natural three-jointdisc and facet complex. Still further, the available artificial discscannot generally be placed or extracted from or to either the anterioror posterior of a patient under treatment as may be medically determinedto be appropriate and, in the case of extraction, without regard forwhether the artificial disc was placed from the anterior or posterior.

With the shortcomings of the prior art in mind, it is therefore anprincipal object of the present invention to improve over the prior artby providing an artificial disc and facet replacement that may be placedor extracted from or to either the anterior or posterior of a patientunder treatment as may be medically determined to be appropriate and, inthe case of extraction, without regard for whether the disc and facetreplacement was placed from the anterior or posterior. Additionally, itis an object of the present invention to provide such an artificial discand facet replacement that also very closely approximates the functionof a natural three-joint disc and facet complex.

SUMMARY OF THE INVENTION

In accordance with the foregoing objects, the present invention—anartificial disc for replacement of a spinal three-joint complex of amammal—generally comprises a generally spinal disc-shaped upper platecomprising an anterior section and a posterior section and a generallyspinal disc-shaped lower plate also comprising an anterior section and aposterior section. The anterior section of the upper plate isselectively separable from the posterior section of the upper plate andthe anterior section of the lower plate is likewise selectivelyseparable from the posterior section of the lower plate. A ball isinterposed the lower face of the upper plate and the upper face of thelower plate and a plurality of posts, each projecting from one of thefaces toward the other of the faces corresponds to a plurality ofdetents provided on the one of the faces opposite the face from whichthe corresponding post projects for engaging the posts.

Finally, many other features, objects and advantages of the presentinvention will be apparent to those of ordinary skill in the relevantarts, especially in light of the foregoing discussions and the followingdrawings, exemplary detailed description and appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Although the scope of the present invention is much broader than anyparticular embodiment, a detailed description of the preferredembodiment follows together with illustrative figures, wherein likereference numerals refer to like components, and wherein:

FIG. 1A shows, in a superior perspective view, the preferred embodimentof the assembled disc and facet replacement of the present invention;

FIG. 1B shows, in an inferior perspective view, the assembled disc andfacet replacement of FIG. 1;

FIG. 2 shows, in a superior plan view, the disc and facet replacement ofFIG. 1;

FIG. 3 shows, in a posterior elevational view, the disc and facetreplacement of FIG. 1;

FIG. 4 shows, in a cross sectional view taken through cut line 4-4 ofFIG. 2, the disc and facet replacement of FIG. 1;

FIG. 5 shows, in a superior perspective view, the disassembled disc andfacet replacement of FIG. 1;

FIG. 6 shows, in a cross sectional view taken through cut line 6-6 ofFIG. 2, details of the preferred embodiment of the section connectionassemblies as employed for selectively joining the anterior andposterior sections each of the upper and lower plates of the disc andfacet replacement of FIG. 1;

FIG. 7 shows, in an enlarged partially exploded cross sectional viewcorresponding to the upper portion of the view of FIG. 6, furtherdetails of a section connection assembly of the disc and facetreplacement of FIG. 1;

FIG. 8 shows, in a partially cut away exploded posterior perspectiveview, details of the anterior portion of a section connection assemblyof the disc and facet replacement of FIG. 1;

FIG. 9 shows, in an posterior plan view, various details of the sectionconnection assembly depicted in FIG. 8 as assembled in the disc andfacet replacement of FIG. 1;

FIG. 10 shows, in a cross sectional view taken through cut line 10-10 ofFIG. 2, details of a first preferred placement between the upper andlower plates of the ball of the disc and facet replacement of FIG. 1;

FIG. 11 shows, in a superior-posterior perspective view of assembledvertebrae, the disc and facet replacement of FIG. 1 as surgically placedwithin a previously prepared intervertebral disc space;

FIG. 12 shows, in a side elevational view, the placement of FIG. 11;

FIG. 13 shows, in a side perspective view, the disassembled disc andfacet replacement of the present invention as implemented with analternative preferred placement between the upper and lower plates ofthe ball; and

FIG. 14 shows, in a cross sectional view generally corresponding to theview of FIG. 10, details of the alternative implementation depicted inFIG. 13.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Although those of ordinary skill in the art will readily recognize manyalternative embodiments, especially in light of the illustrationsprovided herein, this detailed description is exemplary of the preferredembodiment of the present invention, the scope of which is limited onlyby the claims appended hereto. As used herein, reference to ananatomical coordinate such as, for example, anterior, posterior,superior, inferior, sagittal plane, axial plane and the like, should begiven its ordinary meaning with respect to human anatomy and, whenapplied to the disc and facet replacement 20 of the present inventionand/or components thereof should be considered as describing the discand facet replacement 20 as operably positioned as particularly shown inFIGS. 11 and 12. Accordingly, within this frame of reference, referenceto the terms “upper” and/or “lower” should be taken as reference tocomponents generally superior and/or inferior, respectively.

Referring now to the figures, and to FIGS. 1A and 1B in particular, thedisc and facet replacement 20 of the present invention is shown togenerally comprise a substantially planar disc-shaped upper plate 21, asubstantially planar disc-shaped lower plate 47 and a ball 109interposed there between. As shown in the figures, the upper plate 21comprises an anterior section 22 and a posterior section 34 which, aswill be better understood further herein, are selectively separable onefrom the other to facilitate insertion into and/or removal from theintervertebral disc space 113 of a patient under treatment. Likewise,the lower plate 47 comprises an anterior section 48 and a posteriorsection 61, also selectively separable one from the other. As also willbe better understood further herein, a plurality of section connectionassemblies 79 is provided for selectively joining the anterior section22 to the posterior section 34 of the upper plate 21 and for selectivelyjoining the anterior section 48 to the posterior section 61 of the lowerplate 47.

As particularly shown in FIGS. 3 and 4, the lower face 25 of theanterior section 22 of the upper plate 21 is provided near its anterioredge with a preferably reniform, inferiorly projecting post 26.Similarly, the lower face 37 of the posterior section 34 of the upperplate 21 is provided about its posterior edge with a plurality ofpreferably reniform, inferiorly projecting post 39. Additionally, theupper face 49 of the anterior section 48 of the lower plate 47 isprovided near its anterior edge with a preferably reniform slot 50positioned to correspond to and for receiving therein the inferiorlyprojecting post 26 of the anterior section 22 of the upper plate 21.Still further, the upper face 62 of the posterior section 61 of thelower plate 47 is provided about its posterior edge with a plurality ofpreferably reniform slots 69, each slot 69 positioned to correspond toand for receiving therein one of the inferiorly projecting posts 39 ofthe posterior section 34 of the upper plate 21. As will be betterunderstood further herein, the provided posts 26, 39 and slots 50, 69cooperate with the ball 109 interposed the unitary upper plate 21(comprising the adjoined anterior section 22 and posterior section 34)and the unitary lower plate 47 (comprising the adjoined anterior section48 and posterior section 61) to allow limited rotation and flotationbetween the upper plate 21 and the lower plate 47 such that theassembled disc and facet replacement 20 very closely approximates thefunction of a natural three-joint disc and facet complex.

A critical aspect of the present invention is the selective separabilityof the anterior section 22 and the posterior section 34 of the upperplate 21 and the selective separability of the anterior section 48 andthe posterior section 61 of the lower plate 47. While not critical tothe present invention, it is nonetheless highly desirable that the upperplate 21 and the lower plate 47 be provided with means for facilitatingalignment of the anterior section 22 and the posterior section 34 of theupper plate 21 when joining together the anterior section 22 and theposterior section 34 to form the unitary upper plate 21 and means forfacilitating alignment of the anterior section 48 and the posteriorsection 61 of the lower plate 47 when joining together the anteriorsection 48 and the posterior section 61 to form the unitary lower plate47. To this end, as particularly shown in at least FIGS. 1, 2 and 5, theupper plate 21 and the lower plate 47 of the disc and facet replacement20 of the present invention are provided with tongue-and-groovestructures at their respective mating edges. In particular, the anteriorsection 22 of the upper plate 21 is shown to comprise a transverselyoriented tongue 28 projecting from its posterior edge 27. Correspondingto and for receiving the provided tongue 28, a transversely orienteddado 41 is formed in the anterior edge 40 of the posterior section 34 ofthe upper plate 21. Likewise, a transversely oriented tongue 54 isprovided on the posterior edge 53 of the anterior section 48 of thelower plate 47 and a transversely oriented dado 73, corresponding to andfor receiving the tongue 54 of the lower plate 47 is provided on theanterior edge 72 of the posterior section 61 of the lower plate 47. Aswill be appreciated by those of ordinary skill in the art, the providedtongue-and-groove structures are very effective for both obtaining andmaintaining planar alignment of the upper face 23 of the anteriorsection 22 of the upper plate 21 with the upper face 35 of the posteriorsection 34 of the upper plate 21; planar alignment of the lower face 25of the anterior section 22 of the upper plate 21 with the lower face 37of the posterior section 34 of the upper plate 21; planar alignment ofthe upper face 49 of the anterior section 48 of the lower plate 47 withthe upper face 62 of the posterior section 61 of the lower plate 47; andplanar alignment of the lower face 51 of the anterior section 48 of thelower plate 47 with the lower face 70 of the posterior section 61 of thelower plate 47. Although Applicant has found the described structure tobe simple and effective, it should be understood that those of ordinaryskill in the art will recognize that other substantially equivalentalignment obtaining and maintaining means may be provided, any and allof which should be considered within the scope of the present invention.

As previously mentioned, the selective separability of the anteriorsections 22, 48 and the posterior sections 34, 61 of the upper plate 21and the lower plate 47, respectively, is implemented in the preferredembodiment of the present invention by the provision of a plurality ofsection connection assemblies 79. As particularly shown in FIGS. 6 and7, the preferred embodiment of each section connection assembly 79comprises a specially formed connecting rod 80 adapted for insertioninto and between a pair of a plurality of orifices 29, 42 or 55, 74(provided in the upper plate 21 and lower plate 47 of the disc and facetreplacement 20 and each oriented to lie substantially within both asagittal and axial plane as detailed further herein). Additionally, eachsection connection assembly further comprises a specially formed sleeve96 and a locking screw 107 adapted to cooperate with their respectiveconnecting rod 80 and pair of provided orifices 29, 42 or 55, 74 suchthat the produced section connection assembly 80 may be inserted into orremoved from the disc and facet replacement 20 from or to either theanterior or posterior side of the disc and facet replacement 20, therebyenabling placement or extraction of the disc and facet replacement 20from or to either the anterior or posterior of the patient undertreatment as may be medically determined to be appropriate and, in thecase of extraction, without regard for whether the disc and facetreplacement 20 was placed from the anterior or posterior. In thismanner, the disc and facet replacement 20 represents a dramaticimprovement in the art inasmuch as for the first time a surgeon is ablewith ease to extract a previously anteriorly placed disc replacementfrom the posterior, thereby avoiding the greatly increased risk ofrepeated anterior side surgery concomitant scarring adjacent majorarteries and other major structures anterior the affected section 110 ofthe patient's assembled vertebrae 111. Likewise, because the disc andfacet replacement 20 of the present invention is readily disassembledfrom either the anterior or posterior, a surgeon performing an anteriorextraction of a previously posteriorly placed disc replacement may, ifnecessary, free and extract the disc replacement in parts as may benecessary due to bone growth about the previously placed discreplacement.

In the case of an anterior placement of the disc and facet replacement20 of the present invention, the component parts of the disc and facetreplacement 20 are assembled ex vivo prior to placement. In the case ofan anterior extraction of a previously placed disc and facet replacement20 of the present invention, the disc and facet replacement 20 may beextracted in tact or, if necessary to free it from surroundingstructures, the disc and facet replacement 20 may be disassembled insitu and the components thereof removed from the intervertebral discspace 113 piecemeal. In the case of a posterior placement of the discand facet replacement 20 of the present invention, the disc and facetreplacement 20 must, in order to avoid injury to the patient's spinalcord 119 due to the limited distance that the spinal cord 119 may beextracted from within the vertebral canal 118, be placed piecemeal andassembled in situ. Likewise, in the case of a posterior extraction of apreviously placed disc and facet replacement of the present invention,the disc and facet replacement 20 must be disassembled in situ and thecomponents thereof removed from the intervertebral disc space 113piecemeal.

Although, especially in light of this exemplary description, those ofordinary skill in the art will recognize that some steps may beperformed in different order and/or differing manner, assembly ex vivoof the disc and facet replacement 20 of the present invention isgenerally carried out by first inserting an end plug 91 into theanterior end 56 of each of the orifices 55 of the anterior section 48 ofthe lower plate 47 and, likewise, inserting an end plug 91 into theanterior end 30 of each of the orifices 29 of the anterior section 22 ofthe upper plate 21. As particularly shown in FIGS. 6 and 7, each endplug 91 is provided about its circumference 92 with threading 93corresponding to the interiorly threaded bore 59 of the orifices 55 ofthe anterior section 48 of the lower plate 47 as well as to theinteriorly threaded bore 33 of each of the orifices 29 of the anteriorsection 22 of the upper plate 21. In order to facilitate placement orremoval of the end plugs 91, each end plug 91 is provided in the centerof its respective outer face 94 with an Allen, or hex, socket 95 or anyother substantially equivalent drive arrangement such as, for example, asquare socket, slot, or spline socket. Whatever drive arrangement isimplemented, it is preferable that the provided drive arrangement doesnot penetrate through the respective end plug 91 in order to preventbone growth within or infiltration of other matter into the orifices 55through the anterior section 48 of the lower plate 47 or the orifices 29through the anterior section 22 of the upper plate 21. Ifnotwithstanding the foregoing potential complication, however, the endplugs 91 are nonetheless provided with sockets that penetrate completelythrough the end plugs 91, such sockets should be sized to preventinadvertent engagement through the penetrating orifice formed throughthe end plugs 91 of tightening or loosening tools and the socket 84provided on the anterior end 83 of the anterior section 81 of eachconnecting rod 80 (as described in more detail further herein). Finally,in order to permit anterior side disassembly in situ of a previouslyplaced disc and facet replacement 20 of the present invention, it isnecessary that the socket 95 of each end plug 91 be oriented to face theanterior sides of the anterior sections 22, 48.

With the end plugs 91 generally positioned as shown in FIGS. 6 and 7,assembly ex vivo of the disc and facet replacement 20 of the presentinvention continues by inserting the anterior section 81 of a connectingrod 80 into the posterior end of one of the orifices 55 through theanterior section 48 of the lower plate 47, whereafter the connecting rod80 is rotated about its longitudinal axis to engage the threaded shaft82 (conforming to the internally threaded diameter 59 of thecorresponding orifice 55 through the anterior section 48 of the lowerplate 47) with the interiorly threaded bore 59 of the orifice 55 throughthe anterior section 48 of the lower plate 47. Rotation of theconnecting rod 80 is continued until the anterior section 81 of theconnecting rod 80 abuts against the interior face of the previouslyinserted end plug 91. It is noted that the threaded shaft 82 of theanterior section 81 comprises a thread pitch reverse of that forming thethreaded shaft 88 of the posterior section 87 of the connecting rod 80.Likewise, the thread pitch of the internally threaded bore 59 of theorifice 55 through the anterior section 48 of the lower plate 47 isreverse that of the internal threading 98 of the barrel 97 of each ofthe sleeves 96 of the section connection assemblies 79. As a result, thesection connection assemblies 79 operate as turnbuckles to draw togetheror push apart the anterior section 48 of the lower plate 47 and theposterior section 61 of the lower plate 47. While it is necessary thatopposite pitches be provided in the anterior and posterior components asdiscussed, it is not critical that one or the other of the anterior orposterior components be given left or right threading, the particularselection being wholly arbitrary. In any case, and as the threading isshown in the figures, the connecting rod 80 is rotated counterclockwiseto effect insertion of the anterior section 81 of the connecting rod 80fully into the orifice 55 through the anterior section 48 of the lowerplate 47 and into abutment with the interior face of the end plug 91. Tofacilitate rotation of the connecting rods 80 in this or similar steps,each connecting rod 80 is provided on its respective posterior end 89with an Allen, or hex, socket 90 or any other substantially equivalentdrive arrangement such as, for example, a square socket, slot, or splinesocket. Upon completion of this step for the first orifice 55 throughthe anterior section 48 of the lower plate 47, a second connecting rod80 is inserted in identical manner into the remaining orifice 55 throughthe anterior section 48 of the lower plate 47.

With the connecting rods 80 inserted as previously described into theorifices 55 through the anterior section 48 of the lower plate 47, theanterior edge 72 of posterior section 61 of the lower plate 47 isabutted against the posterior edge 53 of the anterior section 48 of thelower plate 47, the posterior sections 87 of the connecting rods 80being received from the anterior into the orifices 74 through theposterior section 61 of the lower plate 47. A sleeve 96 of a sectionconnection assembly 79 is then inserted from the posterior side of theposterior section 61 of the lower plate 47 into one of the orifices 74through the posterior section 61 of the lower plate 47. As particularlyshown in FIGS. 6 through 8, the sleeves 96 of the section connectionassemblies 79 each comprise a barrel 97 having internal threading 98conforming to the diameter of the threading 88 of the posterior section87 of the connecting rods 80 and a smooth outer circumference 99. Thebarrel 97 of each sleeve 96 is further sized to fit snuggly in the spacebetween the threaded shaft 88 of the posterior section 87 of aconnecting rod 80 and a smooth bore 77 forming the orifice 74 throughthe posterior section 61 of the lower plate. The posterior end 100 ofeach sleeve 96 comprises an integral cap 101, the integral cap 101 beingprovided in the central region of its outer face 102 with an Allen, orhex, socket 104 or any other substantially equivalent drive arrangementsuch as, for example, a square socket, slot, or spline socket. Utilizingthe provided drive arrangement 104 (and assuming the choice of threaddirection previously discussed and as shown in the figures), the sleeve96 is rotated clockwise to engage its internal threading 98 with thethreaded shaft 88 of the posterior section 87 of the respectiveconnecting rod 80, thereby seating the integral cap 101 of the sleeve 96into a should 76 provided about the posterior end 75 of the orifice 74through the posterior section 61 of the lower plate 47 and drawing theposterior section 61 of the lower plate 47 tightly against the anteriorsection 48 of the lower plate 47. Upon completion of this step for thefirst orifice 74 through the posterior section 61 of the lower plate 47,a second sleeve 96 is inserted in identical manner into the remainingorifice 61 through the posterior section 61 of the lower plate 47.Finally, in order to stabilize each sleeve 96 in place, which iscritical to ensure that a previously placed disc and facet replacement20 of the present invention may if necessary be disassemble in situ fromthe anterior, the perimetrical region 105 of the outer face 102 of eachsleeve 96 is provided with a plurality of serrations 106 sized toconform to a portion of the head of a locking screw 107 such as, forexample, a flat head socket screw 108. Insertion of a locking screw 107into each of a plurality of threaded holes 78, provided parallel to andslightly radially offset from each orifice 74 through the posteriorsection 61 of the lower plate 47, completes the assembly of the lowerplate 47, the anterior section 48 and the posterior section 61 beingcompletely and securely adjoined to form a unitary lower plate 47.

Temporarily setting aside the integral lower plate 47, assembly ex vivoof the disc and facet replacement 20 of the present invention continuesby inserting the anterior section 81 of a connecting rod 80 into theposterior end of one of the orifices 29 through the anterior section 22of the upper plate 21, whereafter the connecting rod 80 is rotated aboutits longitudinal axis to engage the threaded shaft 82 (conforming to theinternally threaded diameter 33 of the corresponding orifice 29 throughthe anterior section 22 of the upper plate 21) with the interiorlythreaded bore 33 of the orifice 29 through the anterior section 22 ofthe upper plate 21. Rotation of the connecting rod 80 is continued untilthe anterior section 81 of the connecting rod 80 abuts against theinterior face of the previously inserted end plug 91. As was the casewith the lower plate 47, it is noted that the threaded shaft 82 of theanterior section 81 comprises a thread pitch reverse of that forming thethreaded shaft 88 of the posterior section 87 of the connecting rod 80.Likewise, the thread pitch of the internally threaded bore 33 of theorifice 29 through the anterior section 22 of the upper plate 21 isreverse that of the internal threading 98 of the barrel 97 of each ofthe sleeves 96 of the section connection assemblies 79. As a result, thesection connection assemblies 79 operate as turnbuckles to draw togetheror push apart the anterior section 22 of the upper plate 21 and theposterior section 34 of the upper plate 21. While it is necessary thatopposite pitches be provided in the anterior and posterior components asdiscussed, it is not critical that one or the other of the anterior orposterior components be given left or right threading, the particularselection being wholly arbitrary. In any case, and as the threading isshown in the figures, the connecting rod 80 is rotated counterclockwiseto effect insertion of the anterior section 81 of the connecting rod 80fully into the orifice 29 through the anterior section 22 of the upperplate 21 and into abutment with the interior face of the end plug 91.Upon completion of this step for the first orifice 29 through theanterior section 22 of the upper plate 21, a second connecting rod 80 isinserted in identical manner into the remaining orifice 29 through theanterior section 22 of the upper plate 21.

With the connecting rods 80 inserted as previously described into theorifices 29 through the anterior section 22 of the upper plate 21, theanterior edge 40 of posterior section 34 of the upper plate 21 isabutted against the posterior edge 27 of the anterior section 22 of theupper plate 21, the posterior sections 87 of the connecting rods 80being received from the anterior into the orifices 42 through theposterior section 34 of the upper plate 21. A sleeve 96 of a sectionconnection assembly 79 is then inserted from the posterior side of theposterior section 34 of the upper plate 21 into one of the orifices 42through the posterior section 34 of the upper plate 21. As was the casewith the lower plate 47, the barrel 97 of each sleeve 96 is sized to fitsnuggly in the space between the threaded shaft 88 of the posteriorsection 87 of a connecting rod 80 and a smooth bore 45 forming theorifice 42 through the posterior section 34 of the upper plate 21.Utilizing the provided drive arrangement 104 as previously described(and assuming the choice of thread direction previously discussed and asshown in the figures), the sleeve 96 is rotated clockwise to engage itsinternal threading 98 with the threaded shaft 88 of the posteriorsection 87 of the respective connecting rod 80, thereby seating theintegral cap 101 of the sleeve 96 into a shoulder 44 provided about theposterior end 43 of the orifice 42 through the posterior section 34 ofthe upper plate 21 and drawing the posterior section 34 of the upperplate 21 tightly against the anterior section 22 of the upper plate 21.Upon completion of this step for the first orifice 42 through theposterior section 42 of the upper plate 21, a second sleeve 96 isinserted in identical manner into the remaining orifice 42 through theposterior section 34 of the upper plate 21. Finally, in order tostabilize each sleeve 96 in place, a locking screw 107 is inserted intoeach of a plurality of threaded holes 46 provided parallel to andslightly radially offset from each orifice 42 through the posteriorsection 34 of the upper plate 21, thereby completing the assembly of theupper plate 21, the anterior section 22 and the posterior section 34being completely and securely adjoined to form a unitary upper plate 21.

As previously discussed, the provided posts 26, 39 and slots 50, 69cooperate with the ball 109 interposed the unitary upper plate 21 andthe unitary lower plate 47 to allow limited rotation and flotationbetween the upper plate 21 and the lower plate 47 such that theassembled disc and facet replacement 20 very closely approximates thefunction of a natural three-joint disc and facet complex. In a firstpreferred embodiment of the present invention as particularly shown inFIGS. 5 and 10, a defect 68, having a standardized footprint, isprovided on the upper face 62 of the posterior section 61 of the lowerplate 47. In this embodiment, an insert 63 having a perimeter 64 sizedto fit into the standardized footprint of the defect 68 and having asocket 66 (corresponding in size to the ball 109) on its upper face 65is also provided. In this manner, the surgeon placing the disc and facetreplacement 20 of the present invention may select from a plurality ofdiffering height inserts 63 to accommodate during the actual surgicalprocedure for the actual superior-inferior dimension of theintervertebral disc space 113 of a particular patient. In particular,the surgeon may measure the dimension, select an appropriate one of theinserts 63 and place the lower face 67 of the insert 63 into the defect68. The ball 109 may then be positioned between the socket 66 on theupper face 65 of the selected and placed insert 63 and a correspondingsocket 38 (also corresponding in size to the ball 109) provided on thelower face 37 of the posterior section 34 of the upper plate 21.

In a second preferred embodiment of the present invention asparticularly shown in FIGS. 13 and 14, such a defect 57 may also beprovided in the upper plate 21 with a corresponding upper plate insert58. Additionally, as also shown in FIGS. 13 and 14, either or both ofthe defects 57, 68 may be positioned across the adjoining edges 27, 40of the anterior section 22 and posterior section 34, respectively, ofthe upper plate 21 and/or across the adjoining edges 53, 72 of theanterior section 48 and posterior section 61, respectively, of the lowerplate 47. In this case, the upper plate defect 57 will comprise ananterior portion 57 a formed in the lower face 25 of the anteriorsection 22 of the upper plate 21 and a posterior portion 57 b formed inthe lower face 37 of the posterior section 34 of the upper plate 21.Likewise, the lower plate defect 68 will comprise an anterior portion 68a formed in the upper face 49 of the anterior section 48 of the lowerplate 47 and a posterior section 68 b formed in the upper face 62 of theposterior section 61 of the lower plate 47. In any case, it should beunderstood that all combinations of usages of the foregoing describedaspects are contemplated within the scope of the present invention, anyparticular implementation being dependent only upon the particulardynamics of the surgical case.

With the ball 109 sandwiched in place between the unitary upper plate 21and the unitary lower plate 47 with or without implementation of one orboth of the inserts 58, 60, the disc and facet replacement 20 asassembled ex vivo is fully prepared for anterior side placement into theintervertebral disc space 113 of a patient under treatment. The surgeonneed only first prepare the intervertebral disc space 113 by surgicallyremoving the affected intervertebral disc 114 from between the superiorand inferior vertebral bodies 112.

Assembly in situ for a posterior insertion of the disc and facetreplacement 20 of the present invention is preceded by preparation ofthe surgical site by first excising portions of the superior articularprocess 115 from the inferior vertebra and portions of the inferiorarticular process 116 and lamina 117 from the superior vertebra asnecessary to access the intervertebral disc space 113 as shown in FIGS.11 and 12. Assembly in situ then takes place as described ex vivo withthe exception that the constituent parts are laid in place in theintervertebral disc space 113 as assembly takes place. In particular,the anterior section 48 of the lower plate 47 is placed (with end plugs91 inserted and positioned); the connecting rods 80 are inserted (beingplaced about the sides of the patient's spinal cord 119); the posteriorsection 61 of the lower plate 47 is placed; and then the sleeves 96 areaffixed and locked. The lower plate insert 60, if utilized, is thenplaced in the lower plate defect 68 and the ball 109 is placed. Finally,the upper plate 21 is likewise placed and assembled. For posterior sideextraction of the disc and facet replacement 20 of the present inventionthe disc and facet replacement 20 must be disassembled in situ followingthe previously described procedure in reverse order.

Finally, as previously discussed, the present invention contemplatesthat it may under some circumstances be necessary to disassemble in situa previously placed disc and facet replacement 20 for removal of thedisc and facet replacement 20 from the anterior side. In this case(still assuming the threading adopted previously herein), the disc andfacet replacement 20 is disassembled by first removing the end plugs 91by clockwise rotation. The connecting rods 80 are then removed to theanterior by clockwise rotation of the rods 80 from their respectiveanterior ends 83 until the anterior sections 22, 28 pull away andseparate from their respective posterior sections 34, 61. Uponseparation, the component parts of the disc and facet replacement 20 maybe extracted piecemeal.

While the foregoing description is exemplary of the preferred embodimentof the present invention, those of ordinary skill in the relevant artswill recognize the many variations, alterations, modifications,substitutions and the like as are readily possible, especially in lightof this description, the accompanying drawings and claims drawn thereto.For example, stabilizing spikes 24, 36, 52, 71 may be provided on theouter faces 23, 35, 51, 70 of the disc and facet replacement 20 topromote stability of the disc and facet replacement 20 post-placement.Additionally, those of ordinary skill in the art will recognize that themidsection 85 of the connecting rods 80 may comprise a smooth shaft 86in order to limit threading about the rods 80 as may be necessary toensure separation of the anterior sections 22, 28 and posterior sections34, 61 during disassembly of the disc and facet replacement 20. Stillfurther, those of ordinary skill in the art will recognize that whilethe present invention is preferably constructed of polyetheretherketoneother materials such carbon fiber, titanium or any substantialequivalent of any of these materials may be utilized. In any case,because the scope of the present invention is much broader than anyparticular embodiment, the foregoing detailed description should not beconstrued as a limitation of the scope of the present invention, whichis limited only by the claims appended hereto.

1. An artificial disc for replacement of a spinal three-joint complex ofa mammal, said artificial disc comprising: a generally spinaldisc-shaped upper plate comprising an anterior section and a posteriorsection, said anterior section of said upper plate being selectivelyseparable from said posterior section of said upper plate; a generallyspinal disc-shaped lower plate comprising an anterior section and aposterior section, said anterior section of said lower plate beingselectively separable from said posterior section of said lower plate; aball interposed a lower face of said upper plate and an upper face ofsaid lower plate; a plurality of posts, each said post projecting fromone of said faces toward the other of said faces; and a plurality ofdetents for engaging said posts, each said detent corresponding to oneof said posts and being provided on the one of said faces opposite theface from which said corresponding post projects.
 2. The artificial discas recited in claim 1, wherein: at least one said post projects fromsaid lower face of said upper plate; and at least one said detent,corresponding to said post projecting from said lower face of said upperplate, is provided on said upper face of said lower plate and positionedopposite said post projecting from said lower face of said upper plate.3. The artificial disc as recited in claim 2, wherein: each said postprojects from said lower face of said upper plate; and each said detent,corresponding to one of said posts, is provided on said upper face ofsaid lower plate and positioned opposite said corresponding post.
 4. Theartificial disc as recited in claim 1, wherein: at least one said postprojects from said upper face of said lower plate; and at least one saiddetent, corresponding to said post projecting from said upper face ofsaid lower plate, is provided on said lower face of said upper plate andpositioned opposite said post projecting from said upper face of saidlower plate.
 5. The artificial disc as recited in claim 4, wherein: eachsaid post projects from said upper face of said lower plate; and eachsaid detent, corresponding to one of said posts, is provided on saidlower face of said upper plate and positioned opposite saidcorresponding post.
 6. The artificial disc as recited in claim 1,wherein each said post comprises a generally reniform cross section. 7.The artificial disc as recited in claim 6, wherein each said detentcomprises a generally reniform perimeter.
 8. The artificial disc asrecited in claim 1, wherein each said detent comprises a generallyreniform perimeter.
 9. The artificial disc as recited in claim 1,wherein said anterior section and said posterior section of each saidplate is interconnected one to the other with a section connectionassembly, each said section connection assembly comprising a connectingrod inserted into and between said anterior section and said posteriorsection and oriented to lie substantially within both a sagittal planeand an axial plane.
 10. The artificial disc as recited in claim 9,wherein each said anterior section of said plates comprises a first borefor receiving therein an anterior section of one of said connecting rodsand each said posterior section of said plates comprises a second borefor receiving therein a posterior section of one of said connectingrods.